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Disclaimer: Yes I may be a bit insane for replacing a lot without a confirmed diagnosis... but part of me was looking for a big project and part of me just wanted to replace the 'unknowns' from when I bought the car. Wish me luck![/QUOTE]

Luck. And keep us posted.

 

An Opti is a disributor; nothing more, nothing less. While a rotor and rotor cap change is considered "routine maintenance" on a conventional distributor, some expect an Opti to last forever without any maintenance.

At 140,000 miles, my Opti finally gave up the ghost, but if the vent hoses hadn't failed, it would have probably lasted even longer; but that doesn't mean the rotor and rotor cap didn't need to be replaced. The truth was that the rotor and rotor cap desperatively needed replacement; that the engine ran at all, and in fact ran strong, is a testament to how robust a Opti can be. And when it did fail, it failed in a short amount of time. The symptoms closely mirror those you describe.

Spark plug wires, in my experience at least, can degrade significantly in as little as two years; a lot depends on their quality and construction.

You are on the right track with a complete ignition tune up. If nothing else, it will establish a firm baseline from which you can trouble shoot other problems, if any.

good luck. let us know how everything works out.

 

So a brief update...

I tore into the car this weekend. I had everything removed yesterday and ready for inspection with today being clean-up/re-installation (not rushing.) First thing I notice when I get to the opti is it's covered in oily grime... more so than I remember from 10k miles ago with a water pump replacement when I cleaned it Next thing, the vent lines are not there?! At some point in the car's life before my ownership I guess the opti had been replaced by a hack who literally hacked the vacuum/fresh air lines right off the thing. I found this for the vacuum fitting:



Yet another reason why I like to tear into every unknown system on the car when I have any reason whatsoever. So a trip to the auto parts store later and some new vent lines were fabbed up and ready to go.

I thoroughly cleaned all the grime out and began re-assembly. After the new opti went in I was set to replace the plug wires. A little wise part of my brain decided it would be a good opportunity to compression check the car:

Cylinder/Compression:
1. 205
3. 195
5. 195
7. 0
2. 195
4. 185
6. 190
8. 198

So compression seemed all good... wait a minute, what was that at cylinder 7

Turns out the AFR Heads/Hotcam project might not be too far off...

Thoughts?
I tried testing it so many different ways I know that it just won't build compression at all... not even move. The only thing I can think of is a valve is either a) not there or b) bent. I was too frustrated and in need of beer to go further and pull the valve cover and/or head to really nail down the problem.

At least when I get the problem fixed, I'll have a brand new ignition/injection system to go along with it

Maybe this will end-up as a 383 build-up if I find some damage to the #7 cylinder/piston...

 

Pull the driver side valve cover off and see what surprises await you...

Thomas

 

pull the valve cover; inquiring minds want to know.

just my thouhgts; not a complete valve failure; burnt valve maybe; lost a lobe on the cam possible or a rocker arm failure more likely; hopefully it'll be something obvious you can repair without a major tear down (not that I have anything against major teardowns mind you)

 

I might try to pull the cover tonight when I get home from work... no promises though, I have a trip to sao paulo in two days so I need to get ready for that!

 

Curious what you find under the valve cover...

 

Drumroll.....



Bent Intake Valve (or my LT4 has a case of the BIV... as I like to call it)



This doesn't look right



After removal of the rocker arm and tapping the valve with a hammer to get it to bounce back up:



I think it needed a little more motivation to come up all the way... I borescoped the cylinder and compared it to the other seven. It's pretty obvious there was a piston meets valve instance from the witness mark I found. The piston looked ok, just a light hit that was probably enough to knock the valve out of alignment with the seat. The valve still moves down freely, just doesn't seat the rest of the way closed. The borescope didn't show any chunks or obvious signs of a valve breakage, so I think the valve is just slightly bent... regardless the head has to come off now. Why baby? Why?! She must have heard me talking about that new M3, I was just looking! Honest!

Realistically, this was probably either revving the thing too high while it was very hot possibly leading to sticking in the guide/smashing by the piston or the valve floating again per the high rpm + piston = smashy.

 

So now the question is... what next? I know I want AFR 195cc heads with my intake port matched. Aside from that what are your guys opinions? HotCam? Something a little more wild like a lunati voodoo? Exotic Muscle headers always seem gorgeous and can bolt right up to my Corsa catback...

I'm thinking of pulling the block out and re-doing it all. When I borescoped it I saw a witness mark on piston #7 so I know that piston hit the valve. The motor is all stock (rebuilt about 25k miles ago) so it was a pretty strong motor to begin with. Rebuild into a 383 with nice heads and cam NA would make quite some power... I want to here what you guys think.

 

Update:
I pulled the head and found the intake valve seat had popped out, causing the intake valve to bind until a hit by the piston bent it out of the way. I'll post pictures tonight. Time to see if the head is salvageable with a new seat... I'm guessing this was a result of getting the car pretty warm then somehow that cylinder cooled off rapidly during shut-down and dropped the seat out of the head. Anyone else see this before?

 

If the engine was rebuilt 25,000 miles ago,I would go for the Lloyd Elliott package(le2).He can also port match your intake to your heads.But first I would bring that head to a machine shop & have them verify that the head is still good after what happened.Lloyd also will recommend and sell you a cam that will work with your set-up.AFR heads are cool but you can have 400 whp with engine appearing stock.Also install some headers to make the whole set-up perform at best.You will also need a tune after work is done.Upgrade the oil pump spring at same time as work is done so you have "better" oil pressure.Also after everything is done,upgrade radiator(Dewitts) so engine runs at a lower & consistant temp.Go for an electric waterpump while your at it too for even more HP & cooling system efficiancy.I also have never seen a valve damage a piston from coming into contact(interference).Let us know what you decide.I basically told you what I am eventually going to do to my engine plus the ignition parts that will be new.

 

Pics of the progress...
I was actually thinking of heading to Golen for the head and intake re-work. Aside from the piston crown damage from the valve contact, the bottom end seems sound... though it's super tempting to do a 383 build while I have everything off. I'm going to let Chad at Golen know what I found and see if it's salvageable or if I need to shop for new heads There is some carbon-build up in there... hmmm



Piston Crown damage:


Good piston next-door:

 

I've had a couple LT1s apart and yours does not look like a fresh rebuild. (My 50,000 mile stocker still looked new when I pulled the heads for a Head Cam install and even my 160K Impala looked better than yours, with no scoring of the cylinder walls and the cross hatching was still evident. If that short block was mine I'd pull it and do a quality rebuild and I'd send the heads and intake to Concord NC for a 200CC AI package and ported intake.
However, it looks like you like to rev your engine so no matter what you choose to do...ditch the self aligning valve train and go to something with more valvetrain control...NSA rockers and guide plates or shaft rockers.


Good luck.


Mike

 

I see scoring on the #7 cylinder wall, if that engine was rebuilt 25k miles ago, then it looks extremely neglected.

 

Let me clarify the rebuild, it was a re-fresh due to a spun rod-bearing on #7. I couldn't afford the cost or down time of a full blueprinting, new pistons, etc... at the time (this was four years ago) so I had the corvette shop do a refresh without machining the block. I'm paying for it now, but didn't have any other options back then. The car has been immaculately maintained the whole time it's been in my possession. I'm leaning more and more towards pulling the short block. Fortunately I can afford the down-time and the price this time around.